The use of a so-called "chassis dynamometer" with inertial weights to measure the acceleration and deceleration performance of an automobile or other vehicle has long been known (see Knudsen R. F., "Inertia Electronically", ISA Journal, April 1958, Vol. 5. No. 4. pp 52-54). Further dynamometers are described in Patent Specifications Nos. GB-A-1297813, 1604320 and 2149520 and in Roberts J. B., "An Advanced High-Speed Dynamometer for Testing Aircraft Tyres, Wheels and Brakes", read before the Applied Mechanics Group of the Institution of Mechanical Engineers on 10 Apr. 1974.
This invention is concerned with a dynamometer of the above general kind in which a test subject is urged towards a rotatory drum by means of a loading head and provision is made for mechanical means to attach or detach the or each inertia element from a rotating drum and shaft assembly. Thus for tests under high acceleration it may be desirable for the drum and shaft assembly to have a low moment of inertia, whereas under other test conditions it may be desirable to have a greater drum width and inertia. It is understood that the change in drum width and actual inertia may be used in addition to inertia simulation as described by Knudsen or energy control as described in Patent Specification No. GB-A-2149520.
Accordingly, the invention provides a drum shaft assembly for a drum dynamometer including at least one annular inertia element on the shaft and releaseably couplable to the assembly to vary the inertia thereof, wherein the assembly carries first interrupted thread means releaseably engageable with second interrupted thread means rotatably supported in the inertia element, and manipulator means is slideable axially of the drum and shaft assembly between a stand-by position and a working position where it can offer or receive the inertia element, the manipulator means having support means for supporting the inertia element and rotatable key means operable to bring about relative rotation of the first and second interrupted thread means to fasten the inertia element to or to release the inertia element from the assembly.
Other preferred features of the invention are defined in the appended claims to which attention is hereby directed.